A position detector (see Patent Document 1, for example) has been known in the art that detects a change in a position of an object as a change in period of a continuous oscillating motion. The position detector includes a sensor unit, a resistor, a capacitor, and a comparator. The sensor unit includes a coil and an electrical conductor (or, in place of the conductor, a magnetic member) arranged such that an area of an overlap zone therebetween varies as the position of the object changes. The resistor is connected in series with the coil. The capacitor is charged and discharged through a series circuit made of the coil and the resistor. The comparator receives an input of a charging voltage of the capacitor, and charges the capacitor when an output of the comparator is at a high level but discharges the capacitor when the output is at a low level. In the position detector, a resistance of the coil, a resistance of the resistor, a capacitance of the capacitor, and a threshold value of the comparator are set so as to minimise the change in the period at an assumed temperature with respect to a change in at least one value of the resistance of the coil, the resistance of the resistor, the capacitance of the capacitor, and the threshold value of the comparator.
There has also been known a measuring apparatus (see Patent Document 2, for example) that includes a detection coil near which a metal object is allowed to be, a measuring unit that measures a quadrature value and an in-phase value of impedance of the detection coil, and a converter that obtains at least any one or both of a distance and a temperature using a function of distance, temperature, and quadrature value, a function of distance, temperature, and in-phase value, and the measured in-phase value and the measured quadrature value.